The present invention relates to a new and improved apparatus for treating metal melts during continuous casting while enclosing the teeming metal to below the surface of the metal pool in the mold to prevent contact with the ambient atmosphere, covering the surface of the pool with a layer of slag and introducing gases into the teeming metal.
A method of treating the metal with a purging gas during continuous casting in a tundish fitted with a pouring tube or pipe has been disclosed in German petty Pat. No. 7,023,173. The arrangement disclosed in such patent which consists of a blowing orifice in the bottom of the tundish in the vicinity of the pouring nozzle has a very modest purifying effect, since the depth of the bath in a tundish is only about 30 to 40 cms. and therefore offers only a short path for the passage of the gas through the steel melt. Hence, the purifying effect regarding the purging of undesirable gaseous constituents in the melt and the removal of non-metallic occlusions or inclusions is very slight. Moreover, when entering the tundish nozzle the steel may pick up fresh oxidic impurities. The maintenance and insertion of porous purging bricks in the tundish is time-consuming and expensive.
It has already been proposed according to U.S. Pat. No. 3,502,249 to deliver major volumes of gas, which as known are needed for controlling the teeming rate, through the stopper rod to the outlet nozzle of a ladle. As such these large volumes of gas cause the metal jet to spatter and they have no significant purifying effect because they do not enter the metal pool in the mold below its surface. The spattering of the teeming jet entering the atmosphere is intended to be prevented by the provision of an expansion chamber.
In the published French Pat. application No. 2,035,336 it is proposed to pass gas through the porous wall of a pouring nozzle to prevent products of oxidation from being deposited and choking the nozzle, particularly when pouring aluminum-killed steel. The introduction of gas around the periphery of the teeming jet does not result in an intimate comixture of gas and steel so that the purifying effect is very limited. The porosity needed for the admission of the gas weakens the brick and leads to premature wear. Moreover, during service difficulties arise in the supply of the gas.
U.S. Pat. No. 2,005,311 describes the passage of major volumes of gas through the stopper rod of a ladle for the purpose of cooling same. This arrangement also has no purifying effect.
Conventional methods of suppressing oxidic impurities during continuous casting have been unable to prevent coarse and principally fine impurities from being deposited, particularly in the marginal zones to depths of about 11/2 cms., a circumstance which in the further processing of ingots and slabs by rolling necessitates the expense of subsequent scarfing and/or the considerable loss of material involved in machining.